[WIP] Improve functions pushdown

[c2main]

Improve planner/executor when executing distributed query from a UDF execution on workers.

The current WIP patches do:

• allow to execute distributed on already distributed statement.

Also related to #5887 which is fixed with this PR ?

WIP: I use the CI here to get a full coverage.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 66.59%. Comparing base (ab7c13b) to head (0a13e9d).

❗ There is a different number of reports uploaded between BASE (ab7c13b) and HEAD (0a13e9d). Click for more details.

HEAD has 139 uploads less than BASE

Flag	BASE (ab7c13b)	HEAD (0a13e9d)
16_regress_check-pytest	2	0
15_regress_check-pytest	2	0
_upgrade	27	6
15_16_upgrade	2	0
14_15_upgrade	2	0
15_regress_check-columnar-isolation	2	0
14_regress_check-pytest	2	0
16_regress_check-follower-cluster	2	0
15_regress_check-follower-cluster	2	0
14_regress_check-columnar-isolation	2	0
15_regress_check-query-generator	2	0
16_regress_check-query-generator	2	0
15_regress_check-columnar	2	0
14_regress_check-enterprise-isolation-logicalrep-3	2	0
15_regress_check-enterprise-isolation-logicalrep-3	2	0
15_regress_check-enterprise-isolation-logicalrep-2	2	0
14_regress_check-follower-cluster	2	0
16_regress_check-columnar-isolation	2	0
16_regress_check-enterprise-isolation-logicalrep-3	2	0
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16_regress_check-split	2	0
16_regress_check-enterprise-failure	2	0
14_regress_check-query-generator	2	0
14_regress_check-columnar	2	0
14_regress_check-enterprise-isolation-logicalrep-2	2	0
15_regress_check-split	2	0
16_regress_check-enterprise-isolation-logicalrep-2	2	0
15_regress_check-enterprise-failure	2	0
14_regress_check-enterprise	2	0
15_regress_check-enterprise-isolation	2	0
16_regress_check-columnar	2	0
16_regress_check-enterprise	2	0
16_regress_check-vanilla	2	0
14_regress_check-enterprise-isolation	2	0
15_regress_check-enterprise-isolation-logicalrep-1	2	0
15_regress_check-enterprise	2	0
14_regress_check-enterprise-isolation-logicalrep-1	2	0
16_regress_check-failure	2	0
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16_regress_check-multi-mx	2	0
14_regress_check-vanilla	2	0
16_cdc_installcheck	2	0
16_regress_check-enterprise-isolation-logicalrep-1	2	0
14_regress_check-failure	2	0
15_regress_check-multi-mx	2	0
15_regress_check-operations	2	1
16_regress_check-operations	2	1
14_regress_check-operations	2	1
14_regress_check-split	2	0
16_regress_check-enterprise-isolation	2	0
14_regress_check-multi-mx	2	0
15_regress_check-isolation	2	1
14_regress_check-multi	2	0
16_regress_check-isolation	2	1
14_regress_check-isolation	2	1
15_regress_check-multi	2	0
16_regress_check-multi	2	0
15_cdc_installcheck	2	0
15_regress_check-multi-1	2	0
16_regress_check-multi-1	2	0
14_regress_check-multi-1	2	0
15_regress_check-failure	2	0

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7823       +/-   ##
===========================================
- Coverage   89.70%   66.59%   -23.11%     
===========================================
  Files         283      283               
  Lines       60518    60305      -213     
  Branches     7543     7491       -52     
===========================================
- Hits        54287    40162    -14125     
- Misses       4076    17111    +13035     
- Partials     2155     3032      +877